Writer: Kevin Robinson-Avila
VELARDE - Although hundreds of adult apple maggot flies have been found in orchards in some northern counties, consumers are unlikely to bite into any mushy brown apples this season.
"It's an extremely low infestation that hasn't yet affected commercial orchards," said Brad Lewis, an entomologist with both the New Mexico Department of Agriculture and New Mexico State University. "We're attacking the problem just at the right time."
On Sept. 24, the NMDA officially quarantined all apples from Los Alamos, Rio Arriba and Santa Fe counties, forcing growers to certify through direct inspection that their apples are maggot-free before selling or exporting them to other markets, said Lewis, the NMDA's bureau chief of entomology and nursery industries.
The maggot, also known as "railroad worm" because it leaves small bite marks on apple skins that resemble tiny railroad tracks, is a common pest in most of the United States, Mexico and Canada. "We're about the last of the apple-growing states to get them," said Carol Sutherland, an entomologist with the NMDA and NMSU's Cooperative Extension Service.
The maggot first appeared in the Northeast about 200 years ago. It spread to the Midwest a century ago and to the Pacific Northwest about 30 years ago, Sutherland said.
Mature female maggots are actually small fruit flies that emerge in the summer before harvest. After mating, they lay their eggs on apples, and the offspring burrow down into the fruit, Sutherland said. They remain there until the apples begin to ripen, and then feed on the fruit as it softens inside.
"They have no legs, just tiny mouth hooks that they use to slash the fruit and suck up the liquid," Sutherland said. "They wriggle and squirm and tunnel their way through the apple, turning it brown and mushy. A soft rot follows the maggot wherever it goes."
As the maggot matures, it leaves the fruit and burrows into the ground to pupate. It emerges again as a small fruit fly the following summer, Sutherland said.
To determine how far the fly has spread, NMDA set traps in orchards in nine apple-growing counties: Los Alamos, Rio Arriba, Santa Fe, San Juan, Sandoval, Bernalillo, Curry, Lincoln and Grant. It also set traps in some backyard orchards in Doņa Ana County, Lewis said.
"We've found the adult fly in orchards in Los Alamos, Rio Arriba and Santa Fe, but we'll probably find it in more counties before the year is out," he said. "We'll expand the quarantine to any county where it gets established."
However, immature apple maggots have so far only been found in fruit from some backyard orchards in Los Alamos, which bodes well for the current harvest.
"Under the quarantine, all growers must inspect their apples for external signs of the maggot, and cut open a percent of their apples to check for internal signs," Lewis said. "To my knowledge, no commercial growers have yet found a maggot."
Gene Lopez, a Velarde-based grower with 400 apple trees, has already inspected 70 boxes of apples. "I've looked them over carefully outside and I cut a bunch of them open, and I haven't found anything so far," Lopez said. "If we were infested we would be devastated, but we're not. We'll continue to comply with all the regulations that the NMDA sets down for us."
An infestation would be hard on apple growers, who lost most of their fruit to late spring frost in the last two years. This year, growers are expected to harvest between 6 million and 8 million pounds of apples, up from only 2 million in 2003, according to the NMDA. The harvest could earn about $2 million, compared with $553,000 last year.
It is possible that recently hatched maggots are still too small and inactive to detect, Sutherland said. "If they just hatched, it can be difficult to find them because the maggot hasn't had enough time to brown and rot the fruit and create tunnels," she said.
But under the current quarantine, growers are being required to examine many more apples externally and internally than in other maggot-infested states, Lewis said.
"Since we're midway through the season, the quarantine is difficult to implement," he said. "But we're hedging our bets that we'll find the telltale signs of maggot if fruit is infested."
If infested fruit is discovered, growers would have to treat their apples before marketing them, Lewis said. "You can kill maggots with cold treatments by placing infected fruit in refrigerators for up to 40 days," he said. "Processing fruit into other products like cider will also kill maggots."
The NMDA and Extension will concentrate on helping growers to detect and contain the maggot next season through integrated pest management (IPM) programs, Lewis said. IPM relies on broad pest control methods that can include chemical, biological and cultural controls. It emphasizes preventive maintenance such as keeping orchards clean, setting traps for pests and diligently destroying all infected fruit.
"The trick to control is a good detection program and being ready to spray orchards as needed," Lewis said. "Most commercial growers already have IPM programs in place, and if they detect adult fruit flies and are spraying, then it's not a major issue. In the coming seasons, infestations are more likely to hit small orchards and backyard growers, because at that level people are less likely to spray their trees."
In fact, some growers see the maggot's appearance as positive, because it will hold growers to a higher quality standard before sending their apples to market.
"The quarantine forces growers to adopt IPM programs," said Ed Costanza, president of the New Mexico Apple Council. "People will have to monitor their orchards closely and apply pesticides, or use alternative control methods if they're organic growers. I see that as a plus for the industry."
© 2013 New Mexico State University Board of Regents
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